How memory is processed 'may influence risk of PTSD'

Post-traumatic stress disorder and memory is investigated in a new study of a 2001 passenger plane near-disaster, conducted by one of the survivors of that flight. The study identifies a potential risk factor that may help to predict which individuals are most vulnerable to post-traumatic stress disorder.

Flight 236's pilots successfully glided the plane into a rough landing. Although 18 passengers and crew were injured, the incident resulted in no fatalities.

On August 24th, 2001, Air Transat Flight 236 departed Toronto, Canada, for Lisbon, Portugal, with 306 passengers and crew onboard. Unknown to the pilots, an incorrect hydraulic pump had been installed in the engine, which caused chafing between the fuel line and the hydraulic line during the flight.

Over the Atlantic Ocean, this chafing resulted in the rupture of the right fuel line. After losing 8 tons of fuel, the pilots of Flight 236 were alerted to a problem by the plane's instruments. They responded by following standard procedure to route fuel from the left wing tank to the right, but this caused the plane's remaining fuel to leak through the rupture at a rate of about 1 gallon per second.

When the right engine failed, the pilots lowered altitude to 32,000 feet. But when the left engine also flamed out, they had no choice but to maneuver the 200-ton Airbus 330 into a glide and warn passengers and crew to prepare for an ocean ditching. The cabin depressurized, onboard lighting and other systems were lost and a countdown to impact began.

About 25 minutes into the emergency, however, the pilots located a military base on a small island in the Azores and successfully glided Flight 236 into a rough landing. Although 18 passengers and crew were injured, the incident resulted in no fatalities.

Onboard Flight 236 was Dr. Margaret McKinnon, who is now a clinician-scientist at St. Joseph's Healthcare Hamilton and associate co-chair of research in the Department of Psychiatry and Behavioural Neurosciences at McMaster University in Hamilton, Canada.

"Imagine your worst nightmare - that's what it was like," she says of that traumatic experience aboard Flight 236. "This wasn't just a close call where your life flashes before your eyes in a split second and then everything is okay."

New study reports 'two key findings' relating to PTSD and memory

For her study, which is published in the journal Clinical Psychological Science, Dr. McKinnon recruited 15 other Flight 236 passengers. The quality and accuracy of the participants' recollection of the Flight 236 emergency was tested by McKinnon and her colleagues and compared against recollections of two other events - 9/11 and a neutral event from the same time period.

The researchers found that the Flight 236 passengers displayed "tremendously enhanced vivid memories" of the event.

The researchers found that the Flight 236 passengers displayed "tremendously enhanced vivid memories" of the event. Although the researchers claim they were not surprised by this, it is a key finding that challenges other studies, which tend to find that "memory for traumatic events is impoverished."

The team also reported a second key finding when they related quality and accuracy of memory recall to which participants had developed PTSD.

The passengers who developed PTSD recalled a high number of "details external to the main event." These details are defined as recollections that were not specific in time or were repetitions or editorial statements. The participants with PTSD recalled a higher number of these details, compared with both the passengers who did not have PTSD and a control group.

What is more, the PTSD group recalled these details external to the main event across all the events tested, not just the traumatic event. This finding is important as it suggests that it is not simply the memory of the traumatic event itself that is related to PTSD, but also how a person processes memory for events in general.

Dr. Brian Levine, senior author and senior scientist at Baycrest's Rotman Research Institute and the University of Toronto, Canada, says:

"What our findings show is that it is not what happened but to whom it happened that may determine subsequent onset of PTSD."

Therefore, being unable to shut out these external or semantic details when recalling a personally experienced event is related to mental control rather than memory recall. The researchers say this finding adds to growing evidence that altered memory processing may be a risk factor for PTSD.

Next, the researchers will conduct a second component of the study, in which they scan the brains of 10 Flight 236 passengers using functional brain imaging in an attempt to expose the mechanisms at work in this altered memory processing.

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